1. Field of the Invention
The invention generally relates to systems and methods for increasing cardiac output and efficiency. More specifically, the invention relates to systems and methods for reducing distention of one or more chambers of the heart and/or aligning one or more cardiac valves for better closure and coaptation thereof.
2. Related Art
Heart failure syndrome is a highly debilitating and degenerative disorder resulting from damage to the heart muscle. The damage to the heart muscle may be caused by a number of conditions, including coronary artery disease, long standing hypertension, leaky heart valve(s), and infections.
The disease of heart failure is common, lethal, and expensive to treat. An estimated 5.1 million Americans have heart failure with approximately 500,000 new cases diagnosed each year. In 1999, an estimated $20.3 billion in directs costs were spent for the care of heart failure patients. Heart failure is also the most common cause of hospitalization for patients 65 years and older in the United States. The mortality rate is 50% at five years for patients diagnosed with heart failure, and to date, there are limited treatment alternatives available.
Heart failure typically occurs when a weakened heart cannot pump an adequate amount of blood to meet the demands of the body's other organs and tissues. Malfunction of any of the valves within the heart can cause problems effecting the entire circulatory system. A leaky valve, for example, does not close properly and permits blood to flow backward as the heart contracts. As a result, the heart must contract and pump more often to compensate for the insufficient amount of blood supplied to the body by the normal cardiac pumping sequence. Overworking the heart in this manner damages the muscle of the heart and often masks underlying valvular disfunction.
Of the cardiac valves, the mitral valve is most often compromised as the powerful pumping action of the left ventricle tends to cause systolic outward bulging of an ischemic region of the left ventricle free wall. The ventricular wall pulls the entire associated muscle towards the left ventricle apex and laterally outwards. Misalignment of leaflets of the mitral valve and malfunction of the mitral valve thus often occurs. Though not as prevalent, the tri-cuspid valve is also susceptible to misalignment and malfunction due to the less aggressive pumping action of the right ventricle, which pumps blood to the lungs. In either case, coaptation of the leaflets of the cardiac valves is compromised, and cardiac output and efficiency is decreased.
FIGS. 1a-1c show representative stages of progressive deterioration of a heart, wherein FIG. 1 a shows a normal heart H with appropriately sized atrial chambers 1 and 2, and appropriately sized ventricular chambers 3 and 4. FIG. 1b shows slightly enlarged ventricular chambers 3 and 4, and FIG. 1c shows increasingly enlarged ventricular chambers 3 and 4. Ultimately, a complex process of damaging structural and functional changes to the heart results.
Normal cardiac valve closure depends upon the integrity of the myocardium, as well as the valve apparatus itself. The normal mitral valve, for example, is a complex structure comprising leaflets, an annulus, chordae tendineae, and papillary muscles. Any damage or impairment in function of any of these components can render the valve structure incompetent.
Surgical treatments of valvular dysfunction ranges from mitral ring annuloplasty to complete valve replacement using mechanical or tissue-based valve prosthesis. While being generally successful and routine in surgical practice today, these procedures are also costly, highly invasive and have high morbidity and mortality rates associated therewith. The paper “Mitral Valve Repair in the Treatment of Heart Failure” by Michael M. Madani, MD, published in Current Treatment Options in Cardiovascular Medicine 2004, 6:305-311, offers general information regarding valve repair techniques, and is hereby incorporated by reference in its entirety for all purposes.
Other device-based options for treating patients suffering from congestive heart failure include options for re-shaping, reinforcing and/or reducing the heart's anatomical structure. These options may use polymeric, metal, plastic, elastic or other bio-compatible materials providing external support to the heart muscle. Examples of such devices are evident in co-pending U.S. patent application Ser. Nos. 10/881,511 and 10/881, 510 of common assignment herewith, the disclosures of which were filed on Jun. 30, 2004 and are incorporated by reference herein in their entirety. U.S. Pat. No. 6,425,856 similarly provides a cardiac constraint device comprised of a jacket made of biologicalty compatible material. Generally, such external support structures provide general relief to an otherwise compromised heart muscle and help to reduce the propensity of chambers of the heart to distend.
FIG. 1d illustrates an example of a cardiac assist device of the prior art in the form of a jacket 20 providing external support to the heart H. The jacket 20 surrounds a valvular annulus of the heart and at least the ventricular lower extremities of the heart. Once positioned as desired around the heart, the jacket 20 is sutured to the heart. The jacket 20 thus works on a passive, mechanical level to reduce periodic myocardial over-stretch and wall stress, and serves as a constant “reminder” to the heart of how the heart should perform. The jacket, however, does not address localized valve mis-alignment and coaptation concerns that often occur due to myocardial over-stretch and wall stress. Moreover, suturing the jacket 20 around a circumference of the heart is a time-consuming and cumbersome procedure. Further still, precise positioning and securing of the jacket about the heart using endoscopic tools and techniques as the heart is beating has proved challenging.
In view of the above, a need exists for systems and methods that increase cardiac output and efficiency by reducing distention of one or more cardiac chambers while aligning one or more cardiac valves for better coaptation and function thereof.